vscode run all tests (pytest) fails

Run all tests using pytest in vscode fails with following error

platform linux -- Python 3.6.9, pytest-5.0.1, py-1.8.0, pluggy-0.13.1
rootdir: /workspace
plugins: cov-2.8.1
Fatal Python error: Aborted

Error: TypeError: Cannot read property 'testsuites' of null

I have been trying to fix this error by installing various versions of pytest, but it doesnt seem to work.

Even test discovery fails with following error

Test Discovery failed: 
Error: free(): invalid pointer
Fatal Python error: Aborted

Does anyone know why this happens ?

Thank you